The primate fovea, while occupying only a small fraction of the total retinal surface, plays a critical role in visual acuity, form vision, color vision, visual fixation and visual tracking. Among the primate species available for laboratory studies, the rhesus monkey is probably the best animal model for human vision. Single neuron recording experiments in foveal regions of the rhesus monkey's visual cortex have suggested that at least three of the different foveal functions in this animal (form vision, color vision and visual tracking) are mediated by separate populations of cells. In view of the well established importance of inhibitory mechanisms in visual processing, plus recent evidence that visual inhibition is modifiable even in adult animals, it is proposed to examine the response of foveal cortical neurons in awake rhesus monkeys in behavioral contexts designed to maximize or minimize different kinds of visual inhibition. Specifically, the project will concentrate on two foveal functions (color vision and visual tracking) and two cell types (color cells and direction cells). The project asks the question, does a cell behave differently when its responses are relevant to an animal's behavior than when its responses are irrelevant? The major objective is thus to determine the neuronal mechanisms underlying selective attention in the primate brain. Selective attention and modifiable neuronal inhibition are likely to play an important role in abnormalities of human visual perception.